Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.80   6.310%   $197.524   $197.52   $197.50   $197.50  
  Purchase #2 $61.49   4.501%   $64.2577   $64.26   $64.25   $64.30  
  Purchase #3 $22.62   3.217%   $23.3477   $23.35   $23.35   $23.30  
  Purchase #4 $170.63   13.873%   $194.3015   $194.30   $194.30   $194.30  
  Purchase #5 $38.43   11.491%   $42.846   $42.85   $42.85   $42.80  
  Purchase #6 $238.74   12.198%   $267.8615   $267.86   $267.85   $267.90  
  Purchase #7 $42.33   6.528%   $45.0933   $45.09   $45.10   $45.10  
  7 purchase totals = $760.04       $835.2317   $835.23   $835.20   $835.20